1) Field of the Invention
The present invention relates to a plastic optical filter, and particularly to an optical filter formed of an acrylic resin, which has an effect of blocking or attenuating rays in the wavelength range of a near infrared region with high efficiency, excellent luminosity factor-compensating ability and besides an optical low-pass filtering function.
2) Description of the Background Art
Optical filters made of glass, in which a copper ion is incorporated in a special phosphate glass material, have heretofore been used as photometric filters and luminosity factor-compensating filters for cameras. These optical filters made of glass, however, have involved such many problems as they are high in specific gravity and hence heavy, high in hygroscopicity, easy to devitrify with time and difficult to process-or machine and polish upon their production. Under the foregoing circumstances, there has thus been a strong demand for provision of a plastic optical filter which has good properties for an optical filter, and at the same time has an optical low-pass filtering function and moreover is low in specific gravity and hygroscopicity and easy to process or machine and polish upon its production.